1. Field of the Invention
The present invention relates to a phase shifter for use in phased array antennas and a method of manufacturing the same, and more particularly, to a distributed analog phase shifter using an etched ferroelectric film and a method of manufacturing the same.
2. Description of the Related Art
In general, phase shifters are essential core parts of active phased array antennas that trace a satellite to make clear and perfect communications possible on a real-time basis even when the active phased array antennas move in a mobile communication system.
Among such phase shifters, a ferroelectric distributed analog phase shifter controls a phase using a characteristic of a ferroelectric material having a dielectric constant that changes according to the strength of an applied electric field. Since the ferroelectric distributed analog phase shifter is small size and lightweight and has a quick-response characteristic, low dielectric loss, and high power processing capability, it is expected to substitute for currently widely used semiconductor devices.
General ferroelectric phase shifters can be roughly classified into four types: a simple coplanar waveguide (CPW) type, a loaded line type, a type using a variable filter, and a reflective structure type in which variable capacitors are connected to terminals of a coupler.
Conventional ferroelectric distributed analog phase shifters are generally combinations of the CPW type and the loaded line type.
However, in the conventional ferroelectric distributed analog phase shifters, a ferroelectric film having a dielectric constant that changes with an applied voltage occupies the entire surface of a substrate. As a result, a characteristic impedance is significantly changed with a change in a phase velocity that is the most important factor of the ferroelectric distributed analog phase shifter. In other words, since the ferroelectric film having a dielectric constant that changes with an applied voltage is formed over the entire surface of a substrate, the dielectric constant of the ferroelectric film may significantly change, causing changes in not only the phase velocity but also a characteristic impedance. Such changes may have a negative influence upon characteristics of a circuit.
Also, difficulty in extracting design parameters requires a number of repetitive processes. If a high voltage is applied to obtain a desired differential phase shift angle, a large difference in insertion loss occurs due to a change in the applied voltage.